Java中关于AbstractQueuedSynchronizer的入门（二）

AQS是一个同步器的基础类，里面的关键字段：

    //如下关键字段都是volatile类型

    /**
     * Head of the wait queue, lazily initialized.  Except for
     * initialization, it is modified only via method setHead.  Note:
     * If head exists, its waitStatus is guaranteed not to be
     * CANCELLED.
     */
    private transient volatile Node head; //获取锁的链式队列的头

    /**
     * Tail of the wait queue, lazily initialized.  Modified only via
     * method enq to add new wait node.
     */
    private transient volatile Node tail;//获取锁的链式队列的尾

    /**
     * The synchronization state.
     */
    private volatile int state; //记录所的状态

通过如下示例代码进行跟踪查看队列实际细节：

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class AQS {
    public static void main(String[] args) throws Exception {

        final Lock lock = new ReentrantLock();

        lock.lock();
        lock.lock();
        newThread(lock,"lock-1").start();
        Thread.sleep(500);
        newThread(lock,"lock-2").start();
        Thread.sleep(500);
        newThread(lock,"lock-3").start();
        Thread.sleep(500);
　　　　　//断点处，可以在此处进行跟踪
        lock.lock();

        Thread.sleep(5000000);
        lock.unlock();
        lock.unlock();
        lock.unlock();

    }

    public static Thread newThread(final Lock lock,final String threadName ) {
        return new Thread(new Runnable() {

            @Override
            public void run() {
                System.out.println(threadName+"正在获取锁！");
                lock.lock();
            }
        },threadName);

    }

}

注意类的继承细节：

abstract static class Sync extends AbstractQueuedSynchronizer 

static final class NonfairSync extends Sync 

此时细节：

三个线程lock-1，lock-2，lock-3正在队列中等待获取锁。

接下来查看一下lock-1如何存储到等待队列中的：